As is generally known in the art, a hybrid electric vehicle uses an internal combustion engine and a battery power source for power. The hybrid electric vehicle efficiently combines torque of the internal combustion engine and torque of a motor.
The hybrid electric vehicle may be divided into a hard type and a mild type according to a power sharing ratio between the engine and a motor. In the case of the mild type of hybrid electric vehicle (hereinafter referred to as a mild hybrid electric vehicle), an integrated starter & generator (ISG) configured to start the engine or generate electricity according to an output of the engine is used instead of an alternator. In the case of the hard type of hybrid electric vehicle, a driving motor for generating driving torque is used in addition to the ISG. The integrated starter & generator may refer to a hybrid starter & generator (HSG).
The mild hybrid electric vehicle may not provide a driving mode in which torque of the ISG is used as main driving torque, but the ISG may assist torque of the engine according to running states of the vehicle and may also charge a battery through regenerative braking. Accordingly, energy efficiency of the mild hybrid electric vehicle may be improved.
In general, internal combustion engines, which are apparatuses that generate power by receiving air and fuel and burning them in a combustion chamber, include an intake valve for drawing the air and fuel into the combustion chamber and an exhaust valve for discharging exhaust gas formed in the combustion chamber. The intake valve and the exhaust valve are opened or closed by rotation of a camshaft that rotates according to rotation of a crankshaft.
It is required to make timing of opening/closing the valves different in accordance with engine speed, engine load, and the like depending on traveling conditions of a vehicle in order to increase efficiency of the engine.
In particular, the timing of opening/closing the intake valve has a large influence on an efficiency of an engine. That is, when the intake valve is opened in advance, since an overlap period of the valves increases and intake/exhaust inertia flow can be sufficiently used at a high speed, the efficiency of the engine increases, but at a low speed, the efficiency decreases since the amount of remaining gas increases, thus a discharge amount of HC (hydrocarbons) increases.
Therefore, a technology that does not set an overlap period of the valves of a camshaft in accordance with the rotation of the camshaft to appropriately control valve timing in accordance with a driving state of the engine has been developed and applied, and is referred to as a CVVT.
The CVVT apparatus includes a continuously variable valve timing unit, an oil control valve (OCV) that is an oil supply device, an oil temperature sensor (OTS), an oil control valve filter, an oil path, an automatic tensioner, etc.
The OCV is a core device of the CVVT apparatus, and controls the valve opening/closing time by changing a path of engine oil which is supplied from an oil pump and flows in the continuously variable valve timing unit according to control from an engine electronic control unit (ECU).
If the oil control valve is short-circuited, air is over-supplied to the combustion chamber or the engine is stopped.
Conventionally, to solve such problems, a method that increases engine torque by increasing engine RPM has been used. Although an air amount supplied to the combustion chamber, ignition timing, or a fuel amount supplied to the combustion chamber is controlled in order to control the engine torque, a physical time delay to control the air amount, the ignition timing, or the fuel amount occurs, and thus the engine may stop due to the time delay.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.